Improvements in cancer epidemiology and diagnosis can be integrated to facilitate early cancer diagnosis and treatment leading to enhanced survival of individuals in high risk groups. The goal of biochemical and molecular epidemiology is to identify individuals at high cancer risk by obtaining pathobiological evidence of (1) high exposure of target cells to chemical, physical and microbial carcinogens and/or (2) increased oncogenic susceptibility due to inherited or acquired host factors. Advances in laboratory methods have been developed recently for use in combination with analytical epidemiology to identify individuals at high cancer risk. These methods include (1) techniques to assess specific host susceptibility factors, (2) assays that detect carcinogens in human tissues, cells and fluids, (3) cellular assays to measure pathobiological evidence of exposure to carcinogens, and (4) methods to measure early biochemical and molecular responses to carcinogens. This is an important new area of emphasis consisting of multidisciplinary investigations into cancer etiology that combine epidemiological and experimental approaches. Investigations to characterize exposure to carcinogens, which may serve as intermediate or end points on the path to malignancy, to identify measures which halt or reverse this process and to investigate the mechanisms of human carcinogenesis, include (1) analysis of oncogenes and gene polymorphism in the DNA of individuals at high risk to cancers that may be associated with infectious agents or heritable states; (2) evaluation of disturbances in immune function as they may relate to malignancies, particularly those of the hematopoietic system; (3) evaluation of body burden of carcinogens (e.g., carcinogen-DNA adducts) in studies of occupational and general environmental cancer risk factors; (4) analyses of air, water and biological specimens for carcinogenic and mutagenic substances; (5) use of monoclonal antibodies to study tumor-associated antigens; (6) investigation of the relationship between micronutrients and a variety of epithelial cancers; and (7) determination of the role of macronutrients, including dietary fat, and subsequent hormonal changes in increasing risk of breast, endometrial and colon cancer.